The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform

Silvianita - One of the best experts on this subject based on the ideXlab platform.

  • Time and cost analysis of Jacket Structure load out using skidding
    IOP Conference Series: Earth and Environmental Science, 2018
    Co-Authors: Silvianita, R D Pradana, D M Chamelia, W L Dhanistha
    Abstract:

    This paper conducted an analysis to determine time and cost required in the Jacket Structure loadout process using skidding method. Determining normal time and cost in accordance to the company's budget for Jacket Structure loadout process using skidding with CPM. The purpose of this paper is to obtain project schedule with low cost using skidding with CPM to determine the time and cost needed for the Jacket load out. The analysis result of time and cost by CPM for Jacket Structure loadout process using skidding is 9 days with a total cost US$ 68,196.

  • Pushover Analysis Pile of ULA Jacket Platform Towards Earthquake Loads by SNI-1726:2012
    International Journal of Offshore and Coastal Engineeing, 2017
    Co-Authors: Dirta Marina Chamelia, Amarendra B. Prakoso, Silvianita
    Abstract:

    This study aims at analyzing pushover on pile Jacket Structure based on SNI-1726:2012 standards for earthquake loads. Push­over analysis or ultimate strength was performed on ULA Jacket plat­form operated by PHE ONWJ. The Jacket platform is operated in the northwestern part of the Java Sea. Design of earthquake loads on ULA Jacket platform Structure with large seismic accele­ration was obtained. From seismic analysis, dynamic response occurred on ULA Jacket platform is evaluated, with natural struc­ture period of 1.256 seconds. The largest shear base values were in X and Y directions resulted from seismic acceleration of PGA 0.2g. On member check, the critical part happens to be one of the members of WD2, and on joint check, the largest UC occurred on 401L joint, both were due to the aforementioned earth quake ace­leration. Pushover analysis was then performed to obtain the value of RSR (Reserve Strength Ratio). The analysis yields an RSR value which far exceed the limiting criteria of API RP 2A WSD of RSR ≥ 0.8. Therefore it could be concluded that ULA Jacket platform Structure is within the range of low consequence category.

  • Project Delay Analysis on Jacket Structure Construction
    Applied Mechanics and Materials, 2017
    Co-Authors: Silvianita, Dirta Marina Chamelia, Firza Redana, Daniel M. Rosyid, Suntoyo
    Abstract:

    The development process of Jacket Structure is not always in accordance with the planned schedule in advance. Many factors affect the planning failure, among others, the time or the planned schedule, budgeted costs, equipment and material needed, the human resources (manpower) and hours of labor (man hours). The need for a systematic manner or method to overcome the problem of delays in the project. This study analyzes the impact of delays on development projects Jacket Structure in PT. XYZ using the Event Tree Analysis (ETA). Methods Event Tree Analysis (ETA) is an analytical technique used to evaluate the processes and events that lead to the possibility of failure. Results of analysis using the Event Tree Analysis (ETA) showed that the construction project is completed in the fabrication of the Jacket Structure but experiencing delays between 1 day to 8 weeks (2 months). This is caused by several factors and are subject to a fine or a penalty of 0.1% per day of the total contract value of development projects Jacket Structure Rp 64,620,178,000.-. Fines range between Rp 64,620,178.- to Rp 2,843,287,832. -.

  • Evaluation of Delay Factors in Jacket Structure Project
    Applied Mechanics and Materials, 2016
    Co-Authors: Silvianita, Dirta Marina Chamelia, Daniel M. Rosyid, Andika Trisna Putra, Rochani
    Abstract:

    Offshore platforms are used worldwide for drrilling, proceesing and even storage purposes. The offshore platforms can be fixed to the seabed, or can be float. The fixed platform namely Jacket Structure is a complex construction and design. Construction process of the Jacket Structure sometimes is not in accordance with the time schedule. There are many factors affect them, limited time, equipment, materials required, and cost of human resources. In order to analyze the delay factors of a Jacket project requires a systematic approach. This paper will discusses the delay factors of the construction of Jacket Structure using FTA (Fault Tree Analysis). Data is obtained from one fabrication company which involve their experts to identify the contribution of delay project. There are three main factors causing the Jacket project delay namely Long Process of Procurement, Late Schecule of Assembly Structure, and Bad Management.

Erik Lund - One of the best experts on this subject based on the ideXlab platform.

  • Structural optimization with fatigue and ultimate limit constraints of Jacket Structures for large offshore wind turbines
    Structural and Multidisciplinary Optimization, 2017
    Co-Authors: Jacob Oest, René Sørensen, Lars Chr. T. Overgaard, Erik Lund
    Abstract:

    The purpose of the research presented in this paper is to develop and implement an efficient method for analytical gradient-based sizing optimization of a support Structure for offshore wind turbines. In the Jacket Structure optimization of frame member diameter and thickness, both fatigue limit state, ultimate limit state, and frequency constraints are included. The established framework is demonstrated on the OC4 reference Jacket with the NREL 5 MW reference wind turbine installed at a deep water site. The Jacket is modeled using 3D Timoshenko beam elements. The aero-servo-elastic loads are determined using the multibody software HAWC2, and the wave loads are determined using the Morison equation. Analytical sensitivities are found using both the direct differentiation method and the adjoint method. An effective formulation of the fatigue gradients makes the amount of adjoint problems that needs to be solved independent of the amount of load cycles included in the analysis. Thus, a large amount of time-history loads can be applied in the fatigue analysis, resulting in a good representation of the accumulated fatigue damage. A reduction of 40 % mass is achieved in 23 iterations using the CPLEX optimizer by IBM ILOG, where both fatigue and ultimate limit state constraints are active at the optimum.

  • Gradient based structural optimization with fatigue constraints of Jacket Structures for offshore wind turbines
    2015
    Co-Authors: Jacob Oest, Lars Chr. T. Overgaard, Erik Lund
    Abstract:

    In recent years a clear tendency in wind energy industry is to install larger wind turbines further away from coastal areas where wind conditions are more favorable. Generally, this will result in larger support Structures of the wind turbines due to an increase in water depth, wind and wave loads. Performing structural optimization with fatigue constraints of the support Structure may result in lower mass, effectively reducing the cost of the support Structure. Thus, the main objective of this work is to develop and implement efficient gradient based structural optimization of Jacket support Structures with fatigue constraints for preliminary design, where the key challenge is to efficiently deal with numerous non-linear fatigue constraints and very large time-history loads. A gradient based optimization framework has been established and demonstrated on the OC4 UpWind Jacket Structure, which is modeled using a 3D beam finite element program. The loads are based on aero-elastic time-marching multibody simulations of the wind turbine. The diameter and thickness of each steel member in the Structure are optimized to reduce overall mass, while being subjected to constraints formulated by Palmgren-Miner’s linear damage hypothesis. A comparative study on the effectiveness of the adjoint design sensitivity analysis determined from analytical expressions with aggregation functions and an active set strategy has been performed. Sensitivities are verified using a finite difference approach. The findings will give clear indications on effectiveness of different methods to perform fatigue design sensitivity analysis on Structures subjected to large time-history loads, while also offering insight into different optimization formulations of the design problem. In short, this study presents a gradient based method for 3D structural optimization with fatigue constraints capable of application to many high-cycle fatigue driven structural design problems.

Xianming Zhang - One of the best experts on this subject based on the ideXlab platform.

  • effects of small time delays on dynamic output feedback control of offshore steel Jacket Structures
    Journal of Sound and Vibration, 2011
    Co-Authors: Xianming Zhang
    Abstract:

    This paper investigates the effect of a small time-delay on dynamic output feedback control of an offshore steel Jacket Structure subject to a nonlinear wave-induced force. First, a conventional dynamic output feedback controller is designed to reduce the internal oscillations of the offshore Structure. It is found that the designed controller is of a larger gain in the sense of Euclidean norm, which demands a larger control force. Second, a small time-delay is introduced intentionally to design a new dynamic output feedback controller such that (i) the controller is of a small gain in the sense of Euclidean norm and (ii) the internal oscillations of the offshore Structure can be dramatically reduced. It is shown through simulation results that purposefully introducing time-delays can be used to improve control performance.

  • CDC - Effects of small time-delays on dynamic output feedback control of offshore steel Jacket Structures subject to wave-induced forces
    Proceedings of the 48h IEEE Conference on Decision and Control (CDC) held jointly with 2009 28th Chinese Control Conference, 2009
    Co-Authors: Xianming Zhang, Qing-long Han, Dongsheng Han
    Abstract:

    This paper is to investigate the effect of a small time-delay on dynamic output feedback control of an offshore steel Jacket Structure subject to a nonlinear wave-induced self-excited hydrodynamic force. Firstly, a conventional dynamic output feedback controller is designed to reduce the internal oscillations of the offshore Structure. It is found that the obtained controller is of a large gain in the sense of Euclidean norm, which demands a large control force. Secondly, a small time-delay is introduced intentionally to design a new dynamic output feedback controller such that (i) the controller is of a small gain in the sense of Euclidean norm; and (ii) the internal oscillations of the offshore Structure can be dramatically reduced. It is shown through simulation results that purposefully introducing time-delays can be used to improve control performance.

Jasmine Siu Lee Lam - One of the best experts on this subject based on the ideXlab platform.

  • Reliability analysis of offshore Structures within a time varying environment
    Stochastic Environmental Research and Risk Assessment, 2015
    Co-Authors: Yi Zhang, Jasmine Siu Lee Lam
    Abstract:

    The analysis and design of offshore Structures necessitates the consideration of environmental loads. Realistic modeling of the environmental loads is particularly important to ensure reliable performance of these Structures. In this paper, structural reliability analysis of offshore Structures subjected to a time varying environment is investigated. In this work, an extreme value statistical model for the wave height is adopted as a basis for the performance assessment of a Jacket Structure. Due to the changing environment, the model parameters are modeled to be time varying. To deal with this issue, two segmentation algorithms are proposed and applied to the observed data in order to derive piecewise stationary processes for a statistical analysis. The investigation includes the extreme value modeling of the wave height in the characterization of the sea load. The implementation of the segmentation algorithms in the original data eventually leads to approximations of the safety quality of the existing Structure within different time interval. The computed result is developed to reflect the time varying effects in the failure probability of Structures. The results are compared with the traditional extreme values approach in view of the accuracy and information content. The investigation is also extended to a case where the design of the Structure ignores the time varying property.

Michael Muskulus - One of the best experts on this subject based on the ideXlab platform.

  • Global slamming forces on Jacket Structures for offshore wind applications
    Marine Structures, 2018
    Co-Authors: Zhengshun Cheng, Michael Muskulus
    Abstract:

    Abstract This study investigates the global slamming forces due to plunging breaking waves on a Jacket Structure, based on the statistical analysis of the experimental data from the WaveSlam project. Hammer tests and wave tests were conducted in the project, and the data are used to reconstruct the time series of the global slamming force by employing a method based on linear regression. The used wave test data were acquired under one wave condition. A total of 3910 force time series are reconstructed and analyzed statistically to reveal the characteristics of the slamming force. For each force time series, six parameters are introduced to describe it, including the peak force, duration, impulse and rising time, etc. The variability and correlation of these parameters are investigated. The distribution of these parameters is modeled with various probability distributions. The results show the high variability of the slamming force and the importance of statistical analyses. Based on these statistical analyses, the slamming coefficient is estimated from the peak force. For a curling factor of 0.4, the mean slamming coefficient is about 1.29. When considering one standard deviation around the mean, the slamming coefficient varies from 0.70 to 6.78 for a curling factor ranging from 0.1 to 0.5. A representative time series of wave slamming force is obtained by averaging the individual force time series. Accordingly, a 3-parameter triangular force model and a 5-parameter exponential force model are proposed to describe the development of the slamming force in time.

  • Inverse Estimation of Local Slamming Loads on a Jacket Structure
    Journal of Offshore Mechanics and Arctic Engineering-transactions of The Asme, 2017
    Co-Authors: Thorvald C. Grindstad, Michael Muskulus
    Abstract:

    Slamming loads from plunging breaking waves feature a high impulsive force and a very short duration. It is difficult to measure these loads directly in experiments due to the dynamics of the Structures. In this study, inverse approaches are investigated to estimate the local slamming loads on a Jacket Structure using hammer test and wave test data from a model scale experiment. First, a state-of-the-art approach is considered. It uses two deconvolution techniques to first determine the impulse response functions and then to reconstruct the wave impact forces. Second, an easier applicable approach is proposed. It uses linear regression with the ordinary least square technique for the force estimation. The results calculated with these two approaches are highly identical. The linear regression approach can be extended to account for the loads transferred among different locations. This leads to lower and theoretically more accurate estimation of the loads compared to the previous two approaches. For the investigated case, the total impulse due to the wave is 22% lower. The estimated forces by the extended approach have a resolution at the millisecond level, which provides detailed information on the shape of the forces. The approach is an important tool for statistical investigations into the local slamming forces, and further on for the development of a reliable engineering model of the forces.

  • Two Methods for the Inverse Estimation of Local Slamming Loads on a Jacket Structure
    Volume 6: Ocean Space Utilization; Ocean Renewable Energy, 2016
    Co-Authors: Michael Muskulus, Thorvald C. Grindstad
    Abstract:

    This article illustrates two inverse methods to estimate the local slamming forces on a Jacket Structure. The experimental data from the hammer test and the wave test are used as the inputs. One method uses two deconvolution techniques: a conjugate gradient technique to solve the impulse response functions and a weighted eigenvector expansion technique to reconstruct the wave impact forces. The other method uses linear regression with the ordinary least square technique to estimate the wave impact forces. The results calculated with these two different methods are highly identical, which enhances the confidence in the result accuracy. The time series of the reconstructed forces are detailed at a millisecond level, which provides decent information on the shape of the forces. This capability enables the methods to be a very useful tool for the further investigations of the local slamming forces.Copyright © 2016 by ASME